Lower Limb Nerves

Question 1

The spinal cord positioning -

Answer 1

Spinal cord extends from the foramen magnum to approx the level of the disc between vertebrae L1-L2 in adults, although it can end as high as vertebra TX2 or as low as the disc between vertebrate L2-L3.
The distal end of the cord (conus medullaris)
Is cone shaped

Question 2

Spinal cord
What is the cauda equina?

Answer 2

Translation - horses tail
Below the end of the spinal cord, the posterior and anterior roots of lumbar, sacral and coccygeal nerves pass inferiorly to reach their exit points from the vertebral canal.
This terminal cluster of roots is the cauda equina.

Question 3

The lumbar and sacral plexus -
Nerves present -

Answer 3

Lumbosacral plexus isa network of nerves derived from lumbar and sacral roots with each one of them dividing into anterior and posterior branches

Major nerves that orientate from here and leave the abdomen and pelvis to enter the lower limb include:
Femoral nerve
Obturator nerve
Sciatic nerve
Superior gluteal nerve
Inferior gluteal nerve

Question 4

Spinal nerves
Posterior root -

Answer 4

Each spinal nerve is connected to the spinal cord by posterior/anterior roots
Posterior - contains processes of sensory neurons carrying information to the CNS - the cell bodies of the sensory neurons are clustered in a spinal ganglion at the distal end of the posterior root, usually in the intervertebral foramen

Question 5

Spinal nerves
Anterior root -

Answer 5

Each spinal nerve is connected to the spinal cord by posterior/anterior roots
Anterior - contains motor nerve fibres, which carry signals away from the CNS - the cell bodies of the primary motor neurones are in anterior regions of the spinal cord.

Question 6

Spinal nerves
How many pairs of spinal nerves are there?

Answer 6

Approximately 31 pairs of spinal nerves - they’re named according to their position with respect to associated vertebrae
C1-C8 - cervical
T1-T12 - thoracic
L1-L5 - lumbar
S1-S5 - sacral
Co - coccygeal

Question 7

Dermatomes -

Answer 7

Areas of the skin who’s sensory distribution is innervated by the Afferent nerve fibres from the dorsal root of a specific single spinal nerve root
Which is also that portion of a peripheral nerve that ‘connects’ the nerve to the spinal cord

Question 8

What are the main branches of the lumbosacral plexus ?

Answer 8

Femoral nerve
Saphenous nerve (sensory)
Obturator nerve
Sciatic nerve
Tibial nerve
Medial and lateral plantar nerves
Common peroneal nerve
Superficial and deep

Question 9

Position of and describe the nerves of the lumbar plexus-

Answer 9

Formed by the anterior rami of nerves L1-L3 and most of the anterior ramus of L4
It also receives a contribution from the T12 (subcostal) nerve
Main nerves are:
Ilio-hypogastric
Ilio-inguinal
Genitofemoral
Lateral cutaneous nerve of thigh
Femoral
Obturator

Question 10

Lumbar plexus
Femoral nerve -

Answer 10

Arises from anterior rami of nerves L2-L4
Muscular branches negate the iliacus, pectineus,sartorius, rectus femoris, vastus medialis, vatus intermedius, vastus lateralis.

Question 11

Lumbar plexus
Obturator nerve -

Answer 11

Arias from anterior rami of nerves L2-L4
Muscular branches innervate Obturator externus, adductor longus, gracilis, adductor brevis, adductor Magnus muscles and may provide a small branch to pectineus muscle

Question 12

Positioning of the sacral plexus and nerves involved:

Answer 12

Sacral plexus on each side is formed by the anterior rami of S1-S4 and the lumbosacral trunk L4-L5
Main nerves are:
Sciatic nerve, superior gluteal, inferior gluteal, Obturator internus and superior gemellus, Quadratus femoris and inferior gemellus, posterior femoral cutaneous and nerve to piriformis

Question 13

Sacral plexus
Sciatic nerve -

Answer 13

Sciatic nerve is the largest nerve of the body and carries contributions from L4-S3
It leaves the pelvis through greater sciatic foramen inferior to the piriformis muscle, enters and passes through the gluteal region and then enters posterior compartment of the thigh where it divides into its two major branches:
Common fibular nerve
Tibial nerve

Damage to this nerve: piriformis syndrome/sciatica

Question 14

Sacral plexus
What muscles does the sciatic nerve innovate?

Answer 14

All muscles in the posterior compartment of the thigh
The part of the adductor Magnus orientating from the ischium
Skin on the lateral side of the leg and the lateral side and sole of the foot.

Question 15

Sacral plexus
Tibial nerve -

Answer 15

The tibial part of the sciatic nerve, either before/after its separation from the common fibular nerve, supplies branches to all muscles in the posterior compartment of the thigh, EXCEPT short head of biceps which is innovated by the common fibular part

Tibial nerve descends through popliteal fossa, enters posterior compartment of the leg and continues into the sole of the foot

Question 16

Sacral plexus
Tibial nerve innovates -

Answer 16

All muscles in posterior compartment of the leg
All intrinsic muscles in the sole of the foot, including the first two dorsal interossei muscles which also may receive Innervation from the deep fibular nerve
And skin on the posterolateral side of the lower half of the leg and lateral side of the ankle, foot and little toe and skin of the sole of foot and toes

Question 17

Sacral plexus
Common peroneal nerve -

Answer 17

Common peroneal part of sciatic nerve Innervation short head of biceps which femoris in posterior compartment of the thigh and then continues into the lateral and anterior compartments of the leg and onto the foot
It innervates - all muscles in anterior and lateral compartments of the leg
Extensor digitorium brevis on the dorsal aspect of the foot and the first two dorsal interossei muscles in the sole of the foot
Skin over the lateral aspect of the leg and ankle and over the dorsal aspect of the foot and toes

Question 18

Sacral plexus
Sural nerve -

Answer 18

Sensory nerve
Supplies the skin over the lateral side of the lower third of the leg
Derives from branches from both tibial and common peroneal nerves

Question 19

Sacral plexus
Deep peroneal nerve -

Answer 19

Innervates dorsiflexors
- Tibialis anterior
Extensor hallucis longus
Extensor digitorium longus
Peroneus tertius

Question 20

Sacral plexus
Superficial peroneal nerve -

Answer 20

Deep to Peroneus longus
Innervates: Peroneus longus/brevis
Skin over lateral leg
Splits into medial and lateral branches

Question 21

Sacral plexus
Superior gluteal nerve -

Answer 21

Carries contributions from anterior rami of L4-S1, leaves the pelvis through the greater sciatic foramen above the piriformis muscle and innervates:
Gluteus med and min and tensor fascia latae muscle

Question 22

Sacral plexus
Inferior gluteal nerve-

Answer 22

Formed by contributions from L5 to S2
Leaves pelvis through the greater sciatic foramen inferior to the piriformis muscle and enters the gluteal region to supply the gluteus maximus

Question 23

Lower limb arteries
Femoral artery -
Is it palpable?

Answer 23

Begins as external iliac artery passes under inguinal ligament to enter femoral triangle on the anterior aspect of the upper thigh
Femoral artery is palpable in femoral triangle just inferior to inguinal ligament, midway between anterior superior iliac spine and pubic symphysis

Question 24

Lower limb arteries
Popliteal artery -

Answer 24

The continuation of the femoral artery in the anterior compartment of the thigh, and begins as the femoral artery passes posteriorly through the adductor hiatus in the adductor Magnus muscle

Appears in the popliteal fossa on upper medial side under margin of the semi membranous muscle
It descend obliquely through fossa with the tibial nerve and enters posterior compartment of the leg where it ends just lateral to the midline of the leg by dividing into anterior and posterior tibial arteries

Question 25

Can you palpate the popliteal artery ?

Answer 25

It is the deepest of the neurovascular structures in the popliteal fossa and is therefore difficult to palpate
However, a pulse can usually be detected by deep palpation near the midline

Question 26

Palpation
Posterior tibial artery -

Answer 26

Enters foot through tarsal tunnel on medial side of the ankle and posterior to medial malleollus

Question 27

Palpation
Anterior tibial artery -

Answer 27

Anterior aspect of ankle between extensor hallucis longus and 1st tendon of extensor digitorium longus

Question 28

Palpation
Dorsalis pedis -

Answer 28

The continuation of the anterior tibial artery as it crosses the ankle joint
The pulse palpated on dorsal aspect of the foot palpating the vessel against the tarsal bones between tendons of flexor hallucis longus and flexor digitorium longus to the second toe